The amnestic disorders are a group of disorders that involve loss of memories previously established, loss of the ability to create new memories, or loss of the ability to learn new information. As defined by the mental health professional's handbook, the Diagnostic and Statistical Manual of Mental Disorders , fourth edition, text revision (2000), also known as DSM-IV-TR, the amnestic disorders result from two basic causes: general medical conditions that produce memory disturbances; and exposure to a chemical (drug of abuse, medication, or environmental toxin). An amnestic disorder whose cause cannot be definitely established may be given the diagnosis of amnestic disorder not otherwise specified.
The amnestic disorders are characterized by problems with memory function. There is a range of symptoms associated with the amnestic disorders, as well as differences in the severity of symptoms. Some people experience difficulty recalling events that happened or facts that they learned before the onset of the amnestic disorder. This type of
amnesia is called retrograde amnesia. Other people experience the inability to learn new facts or retain new memories, which is called anterograde amnesia. People with amnestic disorders do not usually forget all of their personal history and their identity, although memory loss of this degree of severity occurs in rare instances in patients with dissociative disorders.
Causes and symptoms
In general, amnestic disorders are caused by structural or chemical damage to parts of the brain . Problems remembering previously learned information vary widely according to the location and the severity of brain damage. The ability to learn and remember new information, however, is always affected in an amnestic disorder.
Amnestic disorder due to a general medical condition can be caused by head trauma, tumors, stroke , or cerebrovascular disease (disease affecting the blood vessels in the brain). Substance-induced amnestic disorder can be caused by alcoholism, long-term heavy drug use, or exposure to such toxins as lead, mercury, carbon monoxide, and certain insecticides. In cases of amnestic disorder caused by alcoholism, it is thought that the root of the disorder is a vitamin deficiency that is commonly associated with alcoholism, known as Korsakoff's syndrome. The causes of transient global amnesia, or TGA, are unclear.
In addition to problems with information recall and the formation of new memories, people with amnestic disorders are often disoriented with respect to time and space, which means that they are unable to tell an examiner where they are or what day of the week it is. Most patients with amnestic disorders lack insight into their loss of memory, which means that they will deny that there is anything wrong with their memory in spite of evidence to the contrary. Others will admit that they have a memory problem but have no apparent emotional reaction to their condition. Some persons with amnestic disorders undergo a personality change; they may appear apathetic or bland, as if the distinctive features of their personality have been washed out of them.
Some people experiencing amnestic disorders confabulate, which means that they fill in memory gaps with false information that they believe to be true. Confabulation should not be confused with intentional lying. It is much more common in patients with temporary amnestic disorders than it is in people with long-term amnestic disorders.
Transient global amnesia (TGA) is characterized by episodes during which the patient is unable to create new memories or learn new information, and sometimes is unable to recall past memories. The episodes occur suddenly and are generally short. Patients with TGA often appear confused or bewildered.
The overall incidence of the amnestic disorders is difficult to estimate. Amnestic disorders related to head injuries may affect people in any age group. Alcohol-induced amnestic disorder is most common in people over the age of 40 with histories of prolonged heavy alcohol use. Amnestic disorders resulting from the abuse of drugs other than alcohol are most common in people between the ages of 20 and 40. Transient global amnesia usually appears in people over 50. Only 3% of people who experience transient global amnesia have symptoms that recur within a year.
Amnestic disorders may be self-reported, if the patient has retained insight into his or her memory problems. More often, however, the disorder is diagnosed because a friend, relative, employer, or acquaintance of the patient has become concerned about the memory loss or recognizes that the patient is confabulating, and takes the patient to a doctor for evaluation. Patients who are disoriented, or whose amnesia is associated with head trauma or substance abuse, may be taken to a hospital emergency room.
The doctor will first examine the patient for signs or symptoms of traumatic injury, substance abuse, or a general medical condition. He or she may order imaging studies to identify specific areas of brain injury, or laboratory tests of blood and urine samples to determine exposure to environmental toxins or recent consumption of alcohol or drugs of abuse. If general medical conditions and substance abuse are ruled out, the doctor may administer a brief test of the patient's cognitive status, such as the mini-mental state examination or MMSE. The MMSE is often used to evaluate a patient for dementia , which is characterized by several disturbances in cognitive functioning (speech problems, problems in recognizing a person's face, etc.) that are not present in amnestic disorders. The doctor may also test the patient's ability to repeat a string of numbers (the so called digit span test) in order to rule out delirium . Patients with an amnestic disorder can usually pay attention well enough to repeat a sequence of numbers where as patients with delirium have difficulty focusing or shifting their attention. In some cases the patient may also be examined by a neurologist (a doctor who specializes in disorders of the central nervous system)
If there is no evidence of a medical condition or substance use that would explain the patient's memory problems, the doctor may test the patient's memory several times in order to rule out malingering or a factitious disorder . Patients who are faking the symptoms of an amnestic disorder will usually give inconsistent answers to memory tests if they are tested more than once.
DSM-IV-TR specifies three general categories of amnestic disorders. These are: amnestic disorder due to a general medical condition, substance-induced persisting amnestic disorder, and amnestic disorder not otherwise specified. The basic criterion for diagnosing an amnestic disorder is the development of problems remembering information or events that the patient previously knew, or inability to learn new information or remember new events. In addition, the memory disturbance must be sufficiently severe to affect the patient's social and occupational functioning, and to represent a noticeable decline from the patient's previous level of functioning. DSM-IV-TR also specifies that the memory problems cannot occur only during delirium, dementia, substance use or withdrawal.
There are no treatments that have been proved effective in most cases of amnestic disorder, as of 2002. Many patients recover slowly over time, and sometimes recover memories that were formed before the onset of the amnestic disorder. Patients generally recover from transient global amnesia without treatment. In people judged to have the signs that often lead to alcohol-induced persisting amnestic disorder, treatment with thiamin may stop the disorder from developing.
Amnestic disorders caused by alcoholism do not generally improve significantly over time, although in a small number of cases the patient's condition improves completely. In many cases the symptoms are severe, and in some cases warrant long-term care for the patient to make sure his or her daily needs are met. Other substance induced amnestic disorders have a variable rate of recovery, although in many cases full recovery does eventually occur. Transient global amnesia usually resolves fully.
Amnestic disorders resulting from trauma are not generally considered preventable. Avoiding exposure to environmental toxins, refraining from abuse of alcohol or other substances, and maintaining a balanced diet may help to prevent some forms of amnestic disorders.
See also Dissociative amnesia
American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th ed. text revised. Washington DC: American Psychiatric Association, 2000.
Sadock, Benjamin J. and Virginia A. Sadock, eds. Comprehensive Textbook of Psychiatry. 7th ed. Vol. 2. Philadelphia: Lippincott Williams & Wilkins, 2000.
Corridan, Brian J., S. N. Mary Leung, I. Harri Jenkins. "A Case of Sleeping and Forgetting." The Lancet 357, no. 9255 (February 17, 2001): 524.
Jernigan, Terry L., Arne L. Ostergaard. "When Alcoholism Affects Memory Functions." Alcohol Health & Research World 19 no. 2 (Spring 1995):104-108.
Kesler, Roman, Richard Zweifler. "Confusion and Memory Loss." Patient Care 34, no. 4 (February 29, 2000): 117.
Weiner, Richard D. "Retrograde Amnesia With Electroconvulsive Therapy." Archives of General Psychiatry 57, no. 6 (June 2000): 591.
American Academy of Child and Adolescent Psychiatry. P. O. Box 96106, Washington, D.C. 20090. (800) 333-7636. <www.aacap.org>.
Tish Davidson, A.M.
"Amnestic disorders." Gale Encyclopedia of Mental Disorders. . Encyclopedia.com. (December 17, 2017). http://www.encyclopedia.com/psychology/encyclopedias-almanacs-transcripts-and-maps/amnestic-disorders
"Amnestic disorders." Gale Encyclopedia of Mental Disorders. . Retrieved December 17, 2017 from Encyclopedia.com: http://www.encyclopedia.com/psychology/encyclopedias-almanacs-transcripts-and-maps/amnestic-disorders
Amnestic disorders are conditions that cause memory loss.
Memory is the ability to retain and recall new information. Memory can be subdivided into short-term memory, which involves holding onto information for a minute or less, and long-term memory, which involves holding onto information for over a minute. Long-term memory can be further subdivided into recent memory, which involves new learning, and remote memory, which involves old information. In general, amnestic disorders more frequently involve deficits in new learning or recent memory.
There are a number of terms that are crucial to the understanding of amnestic disorders. In order to retain information, an individual must be able to pay close enough attention to the information that is presented; this is referred to as registration. The process whereby memories are established is referred to as encoding or storage. Retaining information in the long-term memory requires passage of time during which memory is consolidated. When an individual's memory is tested, retrieval is the process whereby the individual recalls the information from memory. Working memory is the ability to manipulate information from short-term memory in order to perform some function. Amnestic disorders may affect any or all of these necessary steps.
The time period affecting memory is also described. Anterograde amnesia is more common. Anterograde amnesia begins at a certain point in time and continues to interfere with the establishment of memory from that point forward in time. Retrograde amnesia refers to a loss of memory for information that was learned prior to the onset of amnesia. Retrograde amnesia often occurs in conjunction with head injury, and may result in erasure of memory of events or information from some time period (ranging from seconds to months) prior to the head injury. Over the course of recovery and rehabilitation from a head injury, memory may be restored or the period of amnesia may eventually shorten.
About 7% of all individuals over the age of 65 have some form of dementia that involves some degree of amnesia, as do about 50% of all individuals over the age of 85.
Causes and symptoms
A number of brain disorders can result in amnestic disorders, including various types of dementia (such as Alzheimer's disease ), traumatic brain injury (such as concussion), stroke , accidents that involve oxygen deprivation to the brain or interruption of blood flow to the brain (such as ruptured aneurysms ), encephalitis, tumors in the thalamus and/or hypothalamus, Wernicke-Korsakoff syndrome (a sequelae of thiamine deficiency usually due to severe alcoholism), and seizures . Psychological disorders can also cause a type of amnesia called "psychogenic amnesia."
A curious condition called transient global amnesia causes delirium (a period of waxing and waning confusion and agitation), anterograde amnesia, and retrograde amnesia for events and information from the several hours prior to the onset of the attack. Transient global amnesia usually only lasts for several hours. Ultimately, the individual recovers completely, with no lasting memory
deficit. The cause of transient global amnesia is poorly understood; researchers are suspicious that it may be due to either seizure activity in the brain or a brief blockage in a brain blood vessel, which causes a brief stroke-like event that completely resolves without permanent sequelae (similar to a transient ischemic attack ).
Symptoms of amnestic disorders may include difficulty recalling remote events or information, and/or difficulty learning and then recalling new information. In some cases, the patient is fully aware of the memory impairment, and frustrated by it; in other cases, the patient may seem completely oblivious to the memory impairment or may even attempt to fill in the deficit in memory with confabulation. Depending on the underlying condition responsible for the amnesia, a number of other symptoms may be present as well.
Diagnosis of amnestic disorders begins by establishing an individual's level of orientation to person, place, and time. Does he or she know who he or she is? Where he or she is? The day/date/time? An individual's ability to recall common current events (who is the president?) may reveal information about the memory deficit. A family member or close friend may be an invaluable part of the examination, in order to provide some background information on the onset and progression of the memory loss, as well as information regarding the individual's original level of functioning.
A variety of memory tests can be utilized to assess an individual's ability to attend to information, utilize short-term memory, and store and retrieve information from long-term memory. Both verbal and visual memory should be tested. Verbal memory can be tested by working with an individual to memorize word lists, then testing recall after a certain amount of time has elapsed. Similarly, visual memory can be tested by asking an individual to locate several objects that were hidden in a room in the individual's presence.
Depending on what types of conditions are being considered, other tests may include blood tests, neuroimaging (CT , MRI , or PET scans of the brain), cerebrospinal fluid testing, and EEG testing.
A neurologist and/or psychiatrist may be involved in diagnosing and treating amnestic disorders. Depending on the underlying condition responsible for the memory deficit, other specialists may be involved as well. Occupational and speech and language therapists may be involved in rehabilitation programs for individuals who have amnestic disorders as part of their clinical picture.
In some cases, treatment of the underlying disorder may help improve the accompanying amnesia. In mild cases of amnesia, rehabilitation may involve teaching memory techniques and encouraging the use of memory tools, such as association techniques, lists, notes, calendars, timers, etc. Memory exercises may be helpful. Recent treatments for Alzheimer's disease and other dementias have involved medications that interfere with the metabolism of the brain chemical (neurotransmitter) called acetylcholine, thus increasing the available quantity of acetylcholine. These drugs, such as donepezil and tacrine, seem to improve memory in patients with Alzheimer's disease. Research studies are attempting to explore whether these drugs may also help amnestic disorders that stem from other underlying conditions.
The prognosis is very dependent on the underlying condition that has caused the memory deficit, and on whether that condition has a tendency to progress or stabilize. Alzheimer's disease, for example, is relentlessly progressive, and therefore the memory deficits that accompany this condition can be expected to worsen considerably over time. Individuals who have memory deficits due to a brain tumor may have their symptoms improve after surgery to remove the tumor. Individuals with transient global amnesia can be expected to fully recover from their memory impairment within hours or days of its onset. In the case of some traumatic brain injuries, the amnesia may improve with time (as brain swelling decreases, for example), but there may always remain some degree of amnesia for the events just prior to the moment of the injury.
Cummings, Jeffrey L. "Disorders of Cognition." In Cecil Textbook of Internal Medicine, edited by Lee Goldman, et al. Philadelphia: W. B. Saunders Company, 2000.
Gabrieli, John D., et al. "Memory." In Textbook of Clinical Neurology, edited by Christopher G. Goetz. Philadelphia: W. B. Saunders Company, 2003.
Mesulam, M.-Marsel. "Aphasias and Other Focal Cerebral Disorders." In Harrison's Principles of Internal Medicine, edited by Eugene Braunwald, et al. New York: McGraw-Hill Professional, 2001.
Rosalyn Carson-Dewitt, MD
"Amnestic Disorders." Gale Encyclopedia of Neurological Disorders. . Encyclopedia.com. (December 17, 2017). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/amnestic-disorders
"Amnestic Disorders." Gale Encyclopedia of Neurological Disorders. . Retrieved December 17, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/amnestic-disorders